Clarke, a geological consultant in Lakewood, Calif., and recently named AAPG Honorary member, knew that induced seismicity isn’t the sexiest topic in the world. And he never intended to develop a lecture on ethics.

“Everyone sees it as an ethics talk, and I never saw it like that,” he said.

As for the popularity of the seismicity lecture, Clarke thinks he has an explanation.

“My personal feeling is that the general public is very interested in anything that has to do with hydrofracturing,” he said.

When Clarke presents his talk, “the conversations afterward have been absolutely incredible,” he noted. Sometimes the discussion sessions last longer than the lecture itself.

Clarke recalled a recent presentation to an industry group.

“The talk goes on for an hour, and we must have gone on for an hour to an hour and a half afterward. It elicited that much thought,” he said.

“The discussion is really much more interesting than the talk, because everybody has an opinion,” he added.

Cause and … Effect?

Induced seismicity is the term commonly used for seismic events, usually tremors or minor earthquakes, caused by human activity. Examples of induced seismicity have been documented and studied since at least the 1920s.

The 11-member NRC committee examined the potential for induced seismicity from the use of multiple energy technologies, including shale gas recovery, carbon capture and storage, geothermal energy production and conventional oil and gas development.

Because the factor most directly correlated with induced seismicity is a change in underground fluid pressure caused by fluids being injected or removed, hydraulic fracturing also was considered as a possible cause.

In its findings, the committee report said:

“The process of hydraulic fracturing a well as presently implemented for shale gas recovery does not pose a high risk for inducing felt seismic events.

“Thirty-five thousand wells have been hydraulically fractured for shale gas development to date in the United States. To date, hydraulic fracturing for shale gas production was cited as the possible cause of one case of felt seismic events in Oklahoma in 2011, the largest of which was M (magnitude) 2.8.

“The quality of the event locations was not adequate to fully establish a direct causal link to the hydraulic fracture treatment. Hydraulic fracturing for shale gas development has been confirmed as the cause of induced seismic events in one case worldwide – in Blackpool, England (maximum M 2.3).”

Induced seismicity “turned out to be the least controversial part of hydrofracturing,” Clarke noted.

Waste-fluid injection wells have gotten the most attention for changing underground fluid pressures and causing seismic events. However, energy technologies do carry the potential for induced seismicity, the NRC committee found, and it recommended steps for further study.

Most induced seismicity produces very small events. Typically, quakes with a magnitude of less than 3 cause no surface damage and are rarely felt by humans, or are felt only slightly.

“At what point does it become a bad thing?” Clarke asked. “I talk about that.”

So Far, So Good

With so much public controversy surrounding hydraulic fracturing, and considering the scientific debate over induced seismic events, Clarke thought someone might stand up at one of his lectures to attack or challenge the committee’s findings.

“I’ve given the talk at least a dozen times, and no one has tried to do that,” he said.

Clarke said Congress was the primary audience for the NRC study, sponsored by the U.S. Department of Energy. Findings also were presented to the White House and presidential staff, and thanks in part to Clarke’s own efforts the report results now have reached a much wider audience.

“I’ve talked with politicians, regulators, everybody. I change the talk as conditions change and other events happen,” he said.

The committee recommendations included steps for government to more closely monitor and assess induced seismicity. Clarke said his lecture audiences usually expect the government to lag in those efforts.

“Actually, quite the contrary,” he noted. “Government has been very good in addressing that.”

As an example, he mentioned efforts in Oklahoma, which at one time had relatively few seismic monitoring stations. The state has acquired new seismographs and is upgrading its seismic monitoring capabilities and adding stations.

A Matter of Trust

As an AAPG Distinguished Lecturer, Clarke presents his talk on induced seismicity by invitation across the United States.

“Right now, I’m booked up to give probably 10 talks,” he said.

But what really needs to happen is for the industry to communicate better about oil and gas activities, in a balanced, open and informative way.

“Our industry needs to talk to the general public to let them know what’s going on,” Clarke said. “The industry itself needs to be as transparent as possible and to be honest in what we say. Trust is involved here.”

Petroleum geologists and others in the industry shouldn’t be afraid to address public concerns, even when controversy is involved, he observed.